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Old 9th September 2010, 11:44 PM   #5921
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In the summer of 1976, we made 100's of measurements, as I said before. In making one measurement, I realized that just flipping a switch on a function generator, could separate IM from TIM in a test. I just turned the switch to a triangle wave, instead of a square wave, which gave a similar harmonic series, BUT dropped the slew rate drastically.
Of course, quibbles from the critics, but it worked really effectively.
We also found that many IC's that were popular AT THE TIME were sort of lousy with the test, especially the UA741, used in studio boards and other pro audio electronics around the world, at the time. I concentrated on a phono stage and what happened. More later.
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Old 10th September 2010, 03:39 AM   #5922
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What was IMPORTANT about the square-triangle comparison test is that we could virtually directly compare SMPTE IM with what the TIM IM test measured, and we could separate the STATIC from the DYNAMIC (TIM or SID) distortions. This gave us great insight to what was wrong with op amps at the time.

When it came to phono preamps, the situation got even more interesting. I modeled a phono preamp similar to a JC-2 phono stage, except that it used an IC for the gain element, rather than a discrete class A design that was in the JC-2.
To make it right, we had to put an RIAA network around the IC, AND we had to put a ANTI-RIAA network between the test oscillator(s) and the input of the phono stage. This is important to make the final output look like the generator output, and to emulate what REAL phono cartridges actually put out because they 'differentiate' the stylus movement, that make them rise in output at 6 dB/octave until they go into mechanical resonance. This got some really interesting results. More later.
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Old 10th September 2010, 06:13 AM   #5923
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When we had done our tests and went our separate ways, 2 papers, at least that I was directly associated with, were presented with a summary of the data we had gathered.
The first was for the AES, and first presented in 1976 at the NY AES Convention by Matti Otala. I recommend that you get a copy if you are interested in TIM, and its formal measurement.
It was published in the JAES, April 1977, Vol. 25, #4 pp. 170-177. The title is:
'A Method for Measuring Transient Intermodulation Distortion (TIM)' Erno Leinonen, Matti Otala, and John Curl

The second article is: 'OMITTED FACTORS IN AUDIO DESIGN' John J. Curl
IEEE 1978. Tulsa Conference. order # CH1285-6/78/0000-0263$00.75@1978IEEE
I highly recommend that you get these two articles through the representative organizations, if you don't have them.
Unfortunately, I cannot at this time send them out, as my computer is still giving me trouble, and I don't know when it will be fixed, so that I can again e-mail info.
However, I feel that attempting to discuss the graphs and charts in these papers will be pointless, as it is technical and my word alone is contested here by the moderators.
So, if anyone is really interested, please get the articles and read them.
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Old 10th September 2010, 01:02 PM   #5924
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http://www.syclotron.com/omittedfactors3.pdf
http://www.jockohomo.net/data/7470.pdf

and interesting too:
http://forums.klipsch.com/forums/sto...4/01162904.pdf
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Old 10th September 2010, 01:09 PM   #5925
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Thanks greatly, gk7. This will seriously help the discussion.
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Old 10th September 2010, 01:13 PM   #5926
iko is offline iko  Canada
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Quote:
Originally Posted by john curl View Post
However, I feel that attempting to discuss the graphs and charts in these papers will be pointless, as it is technical and my word alone is contested here by the moderators.
So, if anyone is really interested, please get the articles and read them.
John please stop referring in general to moderators. Your word has been contested by some of the moderators as much as it was contested by any regular member.
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Old 10th September 2010, 01:17 PM   #5927
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Now that we have real, published graphs and charts in front of us, it might be easier to discuss details about TIM distortion, IM distortion, and maybe even other distortion mechanisms lurking in audio products.
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Old 10th September 2010, 01:19 PM   #5928
SY is offline SY  United States
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Quote:
Originally Posted by ikoflexer View Post
John please stop referring in general to moderators. Your word has been contested by some of the moderators as much as it was contested by any regular member.
Especially ironic considering that I'm hosting the "omitted factors" paper.

It's easier to play martyr than to engage in serious discussion and review.
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Old 10th September 2010, 01:23 PM   #5929
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SY, thank you for hosting the 'Omitted factors' paper. If you wish, we might get Dimitri, the true source of the paper, at least for me, to host it instead.
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Old 10th September 2010, 01:27 PM   #5930
iko is offline iko  Canada
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Guys, just a friendly reminder, let's stick to statements about the papers, the technique, the analysis and let's leave statements about people out of this.
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